- #1

leroyjenkens

- 590

- 48

## Homework Statement

Use (the bac-cab rule) to expand this triple product:

**L**= m

**r**x (

**ω x r**)

If

**r**is perpendicular to

**ω**, show that you obtain the elementary formula, angular momentum = mvr.

(The bold letters are vectors.)

## Homework Equations

**A X (B X C) = (A[itex]\cdot[/itex]C)B - (A[itex]\cdot[/itex]B)C**

## The Attempt at a Solution

Well, simply doing the bac-cab rule, I get

(m

**r**[itex]\cdot[/itex]

**ω**)

**r**- (m

**r**[itex]\cdot[/itex]

**r**)

**ω**

Which isn't even close to the answer in the book, which is:

**L**=m[

**r**-(

^{2}ω**ω [itex]\cdot[/itex]r**)

**r**]

No idea how they got that.

Even if I distribute the

**r**, they don't have it distributed to the

**ω**, and on the right term, they don't distribute the

**ω**. I don't understand.

Thanks